The following relates generally to wireless communication, and more specifically to random access channel (RACH) conveyance of downlink (DL) synchronization beam information for various downlink-uplink (DL-UL) correspondence states.
Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., a Long Term Evolution (LTE) system). A wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE).
Wireless communication systems may operate in millimeter wave (mmW) frequency ranges, (e.g., 28 GHz, 40 GHz, 60 GHz, etc.). Wireless communications at these frequencies may be associated with increased signal attenuation (e.g., path loss), which may be influenced by various factors, such as temperature, barometric pressure, diffraction, etc. As a result, signal processing techniques, such as beamforming, may be used to coherently combine energy and overcome the path losses at these frequencies. Due to the increased amount of path loss in mmW communication systems, transmissions from the base station and/or the UE may be beamformed.
Wireless communications between two wireless nodes, (e.g., between a base station and a UE), may use beams or beam-formed signals for transmission and/or reception. A base station may transmit beamformed synchronization signals on downlink (DL) synchronization beams. A UE may receive a synchronization signal on one or more of the DL synchronization beams, and thus be enabled to initiate a RACH procedure with the base station. In some instances, the UE may send a message to the base station as part of the RACH procedure, and the base station may assume that the uplink (UL) beam on which the RACH message is received is representative of a DL beam which the base station should use in communicating with the UE. In other words, the base station assumes DL-UL correspondence. However, correspondence between the DL channel and UL channel may be missing, for various reasons. Thus, the base station assumption may be incorrect, meaning that the DL beam selected by the base station may not be the most appropriate beam for communications with the UE.